Whips are also largely responsible for arranging the business of parliament. In that capacity, the attack-dogs of party discipline are euphemistically referred to as 'the usual channels'.

The SDLP informally takes the whip of its sister party, Labour, while the DUP whips its eight MPs independently.

MPs who are not whipped are usually the political undead, cast aside by their tribe.

Nadine Dorries is in this position, for a reality TV appearance that she failed to clear with the whips, as is pugilist Eric Joyce, for causing a punch-up in a Commons bar last year.

Two of our MPs take no whip, but far from being political zombies, they are both independent women, who have made their mark at Westminster.

Lady Hermon split with the UUP before the last election over its decision to enter into an electoral pact with the Conservatives.

At the time, she made clear she did not want to take the Tory whip at Westminster and she held on to her North Down seat as an independent unionist.

Naomi Long was in a different position when elected. Alliance is a sister party of the Lib Dems and it would have been natural for her to take its whip and sit on the government benches. But she was canny enough to realise that carried little advantage for her.

Last week, she explained that, as a party of one, she decided to keep her options open. "I am not tied with a government whip or an opposition whip."

On several occasions this session, the Lib Dems have snubbed their Tory coalition partners and either gone into the division lobbies with Labour, or threatened to.

Nick Clegg used this tactic to force David Cameron to compromise on Press regulation and to defeat plans to cut MP numbers.

Parliamentary arithmetic is complex, but, put simply, Labour and the Lib Dems can defeat the Tories, but not if the small parties and independents vote the other way.

In the final two years of this government, we can expect to see the Lib Dems try to maintain what Vince Cable called "equidistance" between Labour and the Tories.

If Nick Clegg sides with Ed Miliband again, Naomi Long and Lady Hermon could one day find themselves holding a casting vote.